Effect of QTRT2 KO on mitochondrial translation. Effect of QTRT2 KO on mitochondrial translation

Mitochondria are organelles that generate most of the energy in eukaryotic cells in the form of ATP via oxidative phosphorylation in eukaryote. Twenty-two species of mitochondrial (mt-)tRNAs encoded in mtDNA are required to translate essential subunits of the respiratory chain complexes involved in oxidative phosphorylation. mt-tRNAs contain post-transcriptional modifications introduced by nuclear-encoded tRNA-modifying enzymes. These modifications are required for deciphering genetic code accurately, as well as stabilizing tRNA. Loss of tRNA modifications frequently results in severe pathological consequences. We performed a comprehensive analysis of post-transcriptional modifications of all human mt-tRNAs, including 14 previously-uncharacterized species, and revised the modification status of some of the previously studied species. In total, we found 17 kinds of RNA modifications at 137 positions (8.7% in 1,575 nucleobases) in 22 species of human mt-tRNAs. An up-to-date list of 34 genes responsible for human mt-tRNA modifications are provided. We here demonstrated that both QTRT1 and QTRT2 are required for biogenesis of queuosine (Q) at position 34 of four mt-tRNAs. Our results provide insight into the molecular mechanisms underlying the mitochondrial decoding system, and could help to elucidate the molecular pathogenesis of human mitochondrial diseases caused by aberrant tRNA modifications. Overall design: Ribosome profiling and RNA-seq

线粒体是真核生物中通过氧化磷酸化以三磷酸腺苷（ATP）形式为真核细胞合成绝大多数能量的细胞器。线粒体DNA（mtDNA）编码的22种线粒体转运RNA（mt-tRNAs），是翻译参与氧化磷酸化的呼吸链复合物关键亚基所必需的。mt-tRNAs存在由核编码的tRNA修饰酶引入的转录后修饰，此类修饰不仅可精准解码遗传密码，还能稳定tRNA结构。tRNA修饰的缺失往往会引发严重的病理后果。本研究对人类所有mt-tRNAs的转录后修饰开展了全面分析，涵盖14种此前未被表征的mt-tRNA种类，并修正了部分已研究的mt-tRNA种类的修饰状态。最终在22种人类mt-tRNAs的1575个核碱基中，共鉴定出17种RNA修饰，分布于137个位点（占总核碱基的8.7%）。本研究提供了一份涵盖34个与人类mt-tRNA修饰相关基因的最新列表。本研究证实，QTRT1与QTRT2两种基因均参与调控4种mt-tRNAs第34位位点的古苷（queuosine, Q）的生物合成。本研究结果为解析线粒体解码系统的分子机制提供了新视角，也有助于阐明由tRNA修饰异常引发的人类线粒体疾病的分子发病机制。整体实验设计：核糖体 profiling（Ribosome profiling）与RNA测序（RNA-seq）